Because of their inherent physical properties and waveguiding capability, single crystal fibers have been shown to have utility in a wide range of optical devices. For example, such fibers can be used in lasers or as sensors in corrosive or high temperature environments where traditional fiber sensors would be inoperative. In the medical field they can be used as a vehicle for delivering radiation to minute target areas. Sapphire (Al.sub.2 O.sub.3) crystal fiber is extremely useful in such applications due to its unique physical properties. Specifically, it has a high melting point, a very low solubility in water, can transmit radiation possessing a wide range of wavelengths (300 nm-4 um), and is strongly resistant to any chemical interaction with its environment.
A known system for growing sapphire fibers was developed at Stanford University and is known as a Laser Heated Pedestal Growth system (hereinafter referred to as the "Stanford System"). This Stanford System is believed to be similar to the system disclosed in U.S. Pat. No. 4,421,721. The operation of the system disclosed in U.S. Pat. No. 4,421,721 involves the initial transformation of a previously generated laser beam having a conventional gaussian intensity profile through its cross sectional area into a laser beam having an annular intensity profile through its cross sectional area via a refraxicon. This laser beam is then focused onto the tip of a solid feed material producing molten feed material. A seed fiber is translated towards this molten feed material and makes contact with this molten feed material. Upon contact, the seed fiber fuses with the molten feed material. The seed fiber fused to the molten feed material is then withdrawn from the molten feed material whereby molten feed material is drawn off in the form of a crystal fiber. However, prior to its translation towards and ultimate fusion with the molten feed material, the seed fiber must be concentrically aligned with the solid feed material in order to produce a high quality crystal fiber. If this alignment is off, the resulting crystal fiber produced will have a non-uniform diameter and hence poor transmission quality. Since the diameters of both the seed fiber and the molten feed material typically range from 100 um to 300 um, this concentric alignment requires great skill on the part of the system's operator. The production of crystal fibers with this system occurs in an air atmosphere at standard atmospheric pressure.
An article co-authored by one of the joint inventors of U.S. Pat. No. 4,421,721 entitled "Characterization of single crystal sapphire fibers for optical power delivery systems" (Appl. Phys. Lett. 55(21), 20 Nov. 1989) provides information regarding the speed at which the Stanford System can grow good optical quality sapphire fibers and their potential application in the medical field. Specifically, the article states the Stanford System "typically" grows good optical quality sapphire crystal fibers at a rate on the order of 4 mm/minute. The article also explained medical applications for sapphire crystal fibers require a crystal fiber with a length of 4 meters. Hence the duration of time needed to grow such crystal fibers with the Stanford System would be approximately 16.7 hours. In applicants' opinion this protracted growth makes the cost of such sapphire crystal fibers prohibitively expensive and ultimately limits their application in medical and other fields.